WO 2013/007633 discloses a control valve for controlling liquid flow in a heating and/or cooling installation under command from an actuator. The control valve comprises a flow regulator with two annular valve members that have an axial overlap. The one valve member is manually rotatable relative to the second valve member. The axially overlapping portions of the valve members define an entry opening with a variable circumferential extent. A third valve member is axially displaceable by the actuator relative to the opening and defines a control edge associated with the opening. Rotation of the first valve member relative to the second valve member changes the circumferential extent of the opening, in order to manually preset a maximum through-flow area. Axial displacement of the third valve member changes the axial extent of the through-flow area of the entry opening, in order to regulate the through-flow area within a range limited by the preset maximum. A differential pressure regulator is provided downstream of the flow regulator, with a pressure chamber arranged between the flow regulator and the differential pressure regulator and it regulates the differential pressure across the entry opening, i.e. the pressure difference between the inlet pressure and the intermediate pressure in the pressure chamber. The exit openings of the differential pressure regulator connect to the outlet of the control valve.
The control valve disclosed in WO 2013/007633 has the advantage that it adjusts itself automatically to a preset flow in order to provide full stroke modulating control by an actuator that acts on the control valve. When the operator presets the valve according to a maximum design flow, the stroke of the third valve member and thus the stroke of the control valve remains the same.
However, control valves like disclosed in WO 2013/007633 have a flow regulator, which closes off very efficiently and have a differential pressure regulator, which in response to the flow regulator closing off simultaneously tries to close off the exit openings when the actuator closes the flow regulator. This has the drawback that an excessive amount of water can be trapped in the pressure chamber between the flow regulator and the differential pressure regulator and this trapped volume of water can in some circumstances obstruct the closing movement of one or the other or both regulators in turn.